Have you ever read the side of a yogurt cup and noticed the words “live and active cultures?” That’s just another word for bacteria! These good bacteria help turn milk into yogurt and they will go straight to your gut to turn food into fuel. There’s been increasing interest in the importance of gut health across the science community, as well as in general health and wellness communities. It’s the most important part of our immune systems because the gut has 70-80% of our immune cells. With that in mind, exploring the potential effects of gut microbiota on various illnesses, from IBS to diabetes, will lead to improved health and patient outcomes. But what about a disease that seems to be more genetic or environmental in nature than other illnesses, such as cancer? Could there be a link between gut bacteria and cancer? 

What is the Gut Microbiome? 

To understand the role of the gut microbiota and cancer, first we need to understand what a microbiome is. The journal Frontiers in Pharmacology defines a microbiome as, “the genetic information inherent in the microbiota itself,” with microbiota being described as the total number of microbial organisms in an area. These microorganisms are bacteria (with some viruses and fungi) and they’re essential for helping our bodies function. Think of it like a vibrant community that works together. The community varies in size, starting from our stomachs down through our intestines. Working with our bodies and each other, the gut microbiome breaks down our food into the energy, vitamins, minerals, proteins, fats, and carbohydrates we need to survive. Additionally, the gut microbiome works to protect itself -and therefore the body it’s residing in- from pathogens. It does this in three different ways.  

1. The bacteria in the gut microbiome sense if there is an excess of bacteria or viruses invading its space. If there are, the residents in that area proliferate and or move to ensure the invaders are unable to adequately colonize and disturb the balance. 
2. Our gut microbiomes assist in maintaining the mucosal lining of our GI tract, helping to keep harmful pathogens from spreading to the rest of our body. This works because the bacteria near the lining of the GI tract are sensitive to messages sent by the rest of our body and alter the environment accordingly to keep the mucosal lining as impermeable as possible to invaders while ensuring the survival of the beneficial gut bacteria, preserving the microbiome within.
3. Finally, the gut microbiome functions as our immune system by signaling for white blood cells, triggering a systemic immune response when necessary. When the gut has to go this far, we will feel physically ill, but it’s all to protect the balance in the microbiome.  

The Gut Microbiome and Cancer Risk 

Healthy vs. Unhealthy Gut: Now that you understand how a healthy gut microbiome is supposed to function, let’s look at what happens when it’s not working that way. Sometimes the mucosal lining is breached and a systemic immune response isn’t enough to regain balance. There are some harmful bacteria that manage to silently take up residence in the microbiome, slowly creating imbalance over time, and creating a chronic problem. When something stays wrong long enough, it can lead to permanent damage. 

Focus on Cancers:  Let’s examine the link between the microbiome and cancer. Approximately one third of GI related cancers result in death, and there is evidence that 20% of all cancers are affected by microorganisms such as gut microbiota. So how does the gut microbiome affect cancer? While most cancer is considered to arise from genetics or the environment, the gut microbiome and cancer share a more intimate relationship than is commonly known. Because of the gut microbiome’s ability to transform so easily to protect itself, it can just as easily protect things that seem to not be causing any immediate problems. It can also protect things that are beneficial to it as a stand-alone microbiome, but not to the individual in which it resides. As fast as the gut microbiome can squash tumor growth, it can also promote it if the DNA coding chains of the microbiome become damaged.  

• Colon cancer: the most common type of cancer. The greatest amount of gut microbiota resides in the colon. Chronic inflammation, poor diet, and overpopulation of certain types of bacteria can trigger gene mutation and cue tumor growth.
• Stomach (gastric) cancer: The stomach’s resident bacteria, Helicobacter pylori, is the main culprit in stomach ulcer creation. Left unchecked, these ulcers disturb the natural microbiome of the stomach, creating gene mutations and causing cancer.
• Esophageal cancer: The esophagus does not have as much microbiotic diversity as the rest of the gastric system, so the simple switch of the resident Streptococcus viridans from being gram positive to gram negative is enough to disturb the balance and trigger gene mutation. 

Bridge the Connection: Damaged DNA in the gut microbiome can result in the production of harmful metabolites, weakened gut barrier function, and altered immune response. 

• Harmful metabolites are small molecules that promote the growth of aberrant DNA. More of these means there is an increased risk of cancer growth.
• Weakened gut barrier function is caused by chronic inflammatory disorders such as Irritable Bowel Disease. The protective barrier of the gut lining becomes thinner, enabling harmful bacteria to create disturbances that can cause cancer in the gut microbiome.
• Because the gut is so closely tied to our immunity, and part of the immune response is to destroy harmful unnatural cells, if this becomes altered it could cause cancer to spread unchecked. 

How Does the Gut Microbiome Influence Cancer?  

It is important that researchers are identifying specific bacteria and viruses that could be related to cancer. Keeping these bacteria in check, or figuring out ways to monitor their levels in the gut microbiome, could give everyone ample warning when the gut microbiome is out of balance, before DNA mutations occur. 

• A metabolite of the Clostridium bacteria, deoxycholic acid, has been linked to colon and liver cancers.
• Toxins produced by Helicobacter pylori are known to cause stomach cancers.
• Antibiotics alter the gut microbiome; prolonged alterations can link cancer and gut microbiome. Additionally, taking antibiotics during cancer treatment can make them less effective.
• Some beneficial bacteria create metabolites such as short-chain fatty acids that have anti-inflammatory and anti-cancer properties.
• Research in mice reveals that where there is more tumor immunosurveillance bacteria, such as the Bifidobacterium species, there is less cancer. 

Role of Gut Microbiota and Cancer Treatment: As it pertains to cancer treatment specifically, a healthy gut microbiome is extremely beneficial. Healthy gut microbiomes work with cancer treatments by: 

• Helping to absorb and utilize medications more readily than imbalanced gut microbiomes.
• Mounting a proper immune response to help the body target and destroy cancer cells.
• Keeping chronic inflammation away, increasing the effectiveness of chemotherapy, and reducing treatment-related side effects.
• Preventing recurrence of cancer by supporting immune response 

Can We Modify the Gut Microbiome for Cancer Prevention? 

Prevention is the first line of treatment for all diseases, but there isn’t enough research to say cancer is entirely preventable. However, there are things we can do to improve our gut microbiomes and that may decrease our likelihood of getting cancer. 

• Stop eating processed foods: Eating food in as natural a state as possible is the best way to get all of the nutrients from it. For example, fresh grapes are healthier than grape jelly. Your body can extract much more nutrition, fiber, and enzymes from a fresh grape than it can from grapes that have been cooked (which kills many beneficial enzymes) and mixed with sugar (your body does not need refined sugar).
• Cut back on sugar: Diets high in sugar gradually deplete the gut’s mucosal lining, eventually resulting in inflammation. Chronic inflammation can lead to changes in cell DNA.
• Eat more Fiber: Fiber provides bulk that sweeps through your intestines, helping keep you from getting constipated. This prevents bad bacteria from settling where it shouldn’t. You need 14g to 30g of fiber a day, depending on your age and gender. Fiber also keeps your cholesterol down and moderates blood sugar. Some fibers, such as apples, can have antioxidants, which are molecules that get rid of unstable molecules (that could cause cancer) found in the body.
• Prebiotics: These foods are fibers and complex carbohydrates such as beans, whole grains, and vegetables. Our microbiomes ferment them to create beneficial metabolites.
• Probiotics: These foods are already fermented and therefore include live bacteria (live and active cultures!) Probiotics can be found in yogurts, Keifer, Kombucha, and kimchi. If none of these sound tasty to you, over-the-counter probiotic capsules are also available.
• Limitations of Probiotics and Prebiotics: Before you go thinking you can take a probiotic pill or eat yogurt every day and have optimal gut health, be aware they each have their limitations. Not every strand of beneficial bacteria will impact every individual the same way; some strains work better for some people, it just depends on the needs of your unique gut microbiome. Additionally, stomach acid can destroy some of the live and active cultures on its journey through your gut, changing the amount of probiotics you had intended for yourself. Finally, if you’re taking probiotic pills, be aware of their shelf life, as their effectiveness decreases over time, and no two probiotics are manufactured the same so there will be differences across brands. 

Current Research and Emerging Therapies  

The role of gut microbiota in cancer treatment is so important that researchers have developed a radical therapy to improve people’s gut microbiomes. Fecal Microbiota Transplant (FMT), involves taking a small amount of feces from a healthy gut microbiome, and transplanting it into an unhealthy one, with the hopes that it acts as a positive catalyst for microbiome-wide change. Fecal donors undergo a rigorous process to ensure they don’t pass on any harmful bacteria to the recipient, but despite testing, there is always a risk. Studies have shown FMT to have an 80%-90% success rate with patients suffering from Clostridium Difficile. People who have IBS and Chrone’s disease have also shown marked improvement, sometimes achieving remission. Where cancer is concerned, this is good news. If chemotherapy has destroyed some of your natural gut microbiome, FMT can help improve it. In addition to helping create healthier gut microbiomes, FMT has made immune checkpoint inhibitors (a type of cancer immunotherapy) more efficient in some cancer patients!  

Important Considerations 

Research on gut microbiome and cancer is still evolving. Every year more information is available about bacteria and how our bodies utilize them. A healthy gut microbiome is important for overall health, but its role in cancer prevention requires further study. Don’t assume just because you eat healthy and have regular bowel movements that you can skip out on recommended colon cancer screenings. 

Conclusion 

While maintaining a healthy gut microbiome will improve your overall health, it can also potentially reduce your cancer risk. Being healthy means taking care of yourself -as per this blog specifically, eating right!- and therefore creating your own personal healthy gut microbiome. If you like chia pets or plants, you can think of it like that; feeding it (your gut) the right foods to make it grow a healthy microbiome. A healthy gut microbiome will supply you with daily energy and defend you in times of need. If you have specific concerns about your gut microbiome and cancer, make sure you discuss your needs with a healthcare professional. If this blog left you wanting more information about gut microbiomes, you can visit the American Gastroenterological Association’s website at https://gastro.org/. They have a wealth of information about all things GI. Don’t neglect your health, be good to your gut. Feed it with real food, not fillers and imitation ingredients.  

References 

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About The Author  

Rachel Peach Fenske, BSN, has worked in healthcare for over a decade, and the past six years as a nurse. Additionally, she is a healthcare freelance writer and cares for her two elderly parents who have multiple health problems. Having worked in many different healthcare settings, Rachel has seen the triumphs and changes the years (and the pandemic) have wrought on the clinical landscape. She feels the current system is failing many people in a myriad of ways, which is what drew her to volunteer for Here to Serve. This non-profit organization makes sure nobody – regardless of their situation – falls through cancer’s healthcare cracks. Here to Serve helps in unique, community-minded ways that empower families, who otherwise would be left floundering amid the life-changing chaos that cancer creates.